MOSCOW, March 10 (Reuters) - Ukraine's Crimea region has invited the Organization for Security and Cooperation in Europe (OSCE) to send a mission to observe Sunday's referendum on joining Russia, Russia's RIA news agency said on Monday.

It said the invitation had been issued to the Vienna-based security and human rights organisation by the region's pro-Russian parliament.

But later in the day, a OSCE spokeswoman said Crimea could not invite observers as the region was not a full-fledged state and therefore not a member of the 57-member organisation.

"As far as we know, Crimea is not a participating state of the OSCE, so it would be sort of hard for them to invite us," she said.

She also said that Ukraine, which is an OSCE member, sent no invitation and that the organisation "respects the full territorial integrity and sovereignty of Ukraine".

For the past week, OSCE military observers have been unable to enter Crimea, which is controlled by Russian forces.

On Monday, Sergei Aksyonov, Crimea's newly appointed Prime Minister contested by central authorities in Kiev, said that the pro-Russian authorities in the region "have cordially asked" OSCE observers to leave.

Ukraine, meanwhile, has asked the Council of Europe human rights watchdog to help investigate the clashes that led to President Viktor Yanukovich's overthrow and to monitor minorities in Crimea.